David Cameron has insisted it will be for voters to decide if Britain remains within the European Union as it emerged that 50 Tory MPs are poised to lead the campaign for Britain to quit.
The Prime Minister said the renegotiation would "make sure that Europe works in Britain's interest" but political parties would not seal the UK's fate in the referendum that follows.
Former Cabinet ministers Owen Paterson and John Redwood are among backers of the newly formed Conservatives for Britain (CfB) that will initially support the premier's bid to renegotiate terms of membership for the UK.
But the group stands ready to lead the charge for exit if the deal the premier secures fails to gain major changes such as regaining control over British laws and free trade powers.
Asked about the CfB as he arrived for the G7 summit in Germany, Mr Cameron said: "What we are having is a renegotiation followed by a referendum. It'll be a renegotiation to make sure that Europe works in Britain's national interest and then the referendum, which won't be for individual parties to decide, it will be for the British public to decide in an in/ out referendum."